Freddie Starr Exploded My Solar Panels

 

Get Used To It - The Mainstream Media Will Not Play Nicely

*An explanation of the above image follows later for younger readers 

An off-duty firefighter notices smoke coming from the roof of a home in Wellingborough and alerts the occupants who safely evacuate the premises.  The fire brigade extinguishes the fire, but only after the whole roof has burned away.  

This story was first reported by The Northants Telegraph, (26th May 2026, 12:26 BST) together with timelapse footage from a doorbell cam on the house opposite taking pictures every few minutes and animating them into a video.

This article reports the incident in a factual way, noting that the house has solar panels installed.

The story was picked up by everyone's favourite tabloid, The Sun, a day later (22:53, 28 May 2026)

In this telling of the story the doorbell footage shows the "terrifying! moment" that the "solar panels EXPLODED! ripping a hole! through the roof" and that the family "scrambled! to safety" as neighbours "watched in horror!"

The Sun article also includes the timelapse footage from the doorbell which, when combined with the misleading headline, does indeed look like the roof exploded.

Next up  the so-called quality press gets involved.  On 8th June The Sunday Times published an article written by Matthew Young of 21 Degrees in its 'Home Help' column offering advice on best practice installation of solar panels.  Matthew noted that solar is an electrical installation and comes with risks similar to those of other electrical appliances in the home, before outlining his advice such as choosing quality products from established manufacturers and having the system designed and installed by a company registered with the Microgeneration Certificaiton Scheme (MCS).  Despite all the sensible content, the article is published under the headline "Should I worry about solar panels exploding in hot weather?"

Meantime, back in the real world, fire investigators from Northampton Fire and Rescue Service return to the site to understand the cause of the fire.  The investigation concludes that the fire was likely due to an electrical fault in the loft, but it was impossible to narrow down the cause further due to challenges with access to the now structurally unsound roof.

So even after the investigation all we really know is that a house with solar panels on it had a fire and the fire started in the loft - maybe from elements of the solar installation, maybe from other electrical equipment.  Can we expect a retraction from the tabloids?  That solar panels don't explode blowing holes in roofs?  Not likely.

An old school friend of mine who had worked on the news desk at the Daily Mail once told me how they would know when their work was done.  Their readership would be too terrified to get out of their beds, at which point he would run a story about the dangers of bedsores.

Just like the bogus headline about a UK comedian putting a friend's pet hamster between two slices of bread to create a tasty late night snack, the news cycle has already moved on by the time the truth emerges.  People remember that solar panels can explode suddenly and our industry is just a little bit worse off.

What should the Solar Industry do?

We need to recognise two irrefutable facts.

1. There will be fires on more and more buildings that have a solar installation.  

The number of homes and commercial buildings with solar has grown to become a meaningful proportion of all buildings (more than 2 million solar installations in the UK).  Some of these buildings will suffer from fires - whether started by the solar or not, but people still see the 'new' thing on the roof and reach for a quick explanation - or maybe in the case of some of our national press, an explanation that fits in with a particular world-view.  The number of stories like this will grow.

2. In some cases the solar installation will be the cause of the fire.

Solar is a very safe technology, but a solar PV installation is an electrical installation and has all the risks that come with that, and perhaps adds in a few more of its own.  Solar remains energised while the panels have daylight, and the DC current side suffers from higher arcing risks due to the comparative stability of the DC arc.

An Action Plan for the Solar Industry

1. Reach a consensus on current best practice for fire safe solar installations, promote its uptake across the industry.  There is already work going on in this area, notably by Jonathan Bates at  Solar Energy UK and the team reviewing the RC62 document. 

2. Consider adopting as mandatory some of these best practice measures through changes to MCS standards.

3. Gather quantitative evidence on the relative fire risks from solar installations.  The most recent studies are more than 10 years old and the technology has evolved greatly since then.  The recently launched PV-FIN initiative is building evidence on the causes of fires involving solar equipment.  Crucially this work aims to add near-miss evidence, which is especially useful since collecting meaningful physical evidence from the aftermath of a well developed fire is difficult.  This work should be welcomed by the industry and its findings, when they come, studied carefully before further updating the best practice guides.

What the industry cannot do is just hope that the news cycle moves on and reporting of "solar fires" will be forgotten.  Parts of the UK media continue to promote negative news about electric vehicles, heat pumps and utility scale solar.  These outlets are unlikely to let the facts get in the way of a good story that is damaging to the solar industry.

*Freddie Starr was a stand up comedian and entertainer in the UK at his peak of fame in the 1970s.  In 1986 one of the best-known British tabloid newspaper headlines of all time featured Starr. The Sun ran its front page with "Freddie Starr Ate My Hamster". The man behind the hamster story was Starr's agent, the British publicist, Max Clifford - at that time Starr's agent.

Future Homes Standard - Homes that Cannot Meet the 40% Solar Requirement

 

The Future Homes Standard (FHS) will make solar PV panels mandatory on all new homes from 2027, with the government announcing that panels will have an area of at least 40% of the ground floor area of the building.  

In this article I'll take a look at how the calculation works, what amount of solar it might result in and how exceptions are dealt with when roofs don't have enough room.  I'll also share an early estimate of how many houses might not be able to meet the requirement in full.

How Much Solar?

The actual requirement for the amount of solar is, quite rightly defined in terms of the total rated power, which means that if you use higher performance panels, you can reduce the area or conversely if the panels you use are of low power rating then a greater area must be installed.  

The actual target is to install solar PV that has the same annual output as a solar array with the following characteristics: an area of 40% of the ground floor area, a specific power of 0.22 kWp/m2, facing SE or SW at a pitch angle of 45 degrees and with little or no shading.

So for an 85 m2 semi detached home, arranged across two floors we might have 42.5m2 of ground floor area and a target solar installation of:

40% x 42.5 x 0.22 = 3.74kWp

This figure could be met for example with ten 405Wp solar panels, or nine 445Wp panels.  It's worth noting that the current average installation we see under Part L 2021 is between four and five panels per house, so the Future Homes Standard represents a rough doubling in the quantity required.

Any amount by which the solar provided exceeds the target counts towards achieving the overall energy targets for the building, so there are benefits to going higher if the roof can fit more.

What About Complex Roofs?

The regulations makes allowances for roofs that are an interesting shape or that have features that limit the amount of solar that is possible, and this is outlined in Appendix B9.  The developer must provide evidence to the building control body to show that it is not possible to install sufficient solar on the roof to meet the requirement.

Roof diagrams showing the roof with and without solar panels showing that the installation provides the maximum PV capacity and annual generation possible for the roof orientation and layout must be provided.

The diagram showing the maximum possible roof area for solar PV has to be made using specific guidance given on the minimum allowable offset distances from other roof features.

An example of a suitable diagram showing the maximum solar possible on a house is shown at the top of the page.

The target for solar PV then becomes a system that produces an amount of energy each year that matches that of a system with the area of solar in the drawing, a specific panel power of 0.22kWp/m2 and the orientation and angle of the actual roof pitches.  This figure is then also used in the Notional House specification so there is no penalty there for having to use a smaller solar system.

At present there are no restrictions on how close to roof edges a solar panel installation can be made (subject to having a sufficient wind resistance to install in an edge zone and a sufficient fire rating to install adjacent to a party wall).  Consequently it might be possible to provide a B9 drawing showing a maximum solar area, and install something different -  so long as it matches or exceeds the annual power generation 

For example this could be achieved by using higher efficiency panels than those in the standard, and covering more of the most advantageous roof pitch, while dropping solar off the less advantageous roof pitches, to meet or exceed the annual energy yield of the B9 drawing.

However, on the same day that the FHS was revealed, the Health and Safety Executive opened a consultation on Approved Document B - the building regulations for fire safety.  This includes what would become mandatory provisions for minimum offset distances for solar panels, so reducing the possibility to use tighter margins to outperform the regulated max-fit.

Something that has been missed in the guidance is to define what size of solar panel should be used in the assessment. This really needs to be clarified because otherwise people will get very different outcomes depending on what panel size is chosen. 

How different panel sizes give different maximum-fit outcomes

 I have discussed this point with colleagues at the Future Homes Hub and the plan is to develop an industry guide in conjunction with representatives from building control bodies to fill in some of the missing detail from Appendix B9.  This way we can hopefully have a consistent approach across industry.

What Proportion of Homes Will Fit 40%

As part of our work at Viridian Solar in support of our housebuilder partners, the design team has performed studies on sample developments to assess which house types can meet a 40% requirement and which cannot.

So far we have seen around 80% of houses on a typical site can fit the full requirement of solar panels on the best elevation.  Of the houses that could not fit the requirement, on average one half of the requirement could be fit on the best elevation, so around 20% of the ground floor area. 

Under the approach in Appendix B9, these homes would need to use all the possible other elevations as well as the best elevation to maximise the solar generation possible, including North facing elevations if necessary.  Depending on the size of the less advantageous roof pitches, this might result in a greater number of solar panels being used due to the penalty that comes as panel orientation moves further away from South facing.  

Of course, this analysis was done before the final regulations were published, and so was using our own manufacturers' guidelines on offset distances which are tighter than those in the FHS.  It is likely that a higher proportion of houses will struggle to meet the 40% target using the Appendix B9 guidance.  No doubt the design team will continue to be working with housebuilders re-evaluating their house types to the final version of the standard.  I will post an update when we have got more data from this work.

When will Homes be Built to the Future Homes Standard?

 

Accompanied by much excitement in the solar industry, the Future Homes Standard (FHS) consultation response was finally published on 24th March 2026, and little wonder because the new regulations make renewable electricity generation (solar PV) mandatory on nearly all new homes.  But how long will it take for the new regulations to feed through into bricks and mortar on the ground, and more importantly solar panels on the roof?

The transitional arrangements published alongside the new regulations give developers some breathing room to get themselves ready to deliver the new specification at scale.  The rules come into force in 12 months.  From March 24th 2027, any new development that applies to Building Control for approval will see all homes on that site built to the new regulations.

A second deadline follows in March 2028.  After this, all homes not yet "commenced" will need to be meet the FHS, irrespective of when the Building Control application was lodged.

The transitional arrangements are identical to those that applied to the last update to the building regulations for energy efficiency - Part L 2021.  So we can use the last building regulations transition as a model for the next. 

What Went Before - Part L 2021

Part L 2021 was announced in that year, with a start date of July 2022 for new sites and July 2023 for houses not yet commenced.  The graph at the top shows the number of housing starts in England (black line) and completions (blue line) from 2018 to 2025.

The solid orange line shows the number of housing completions that were built to Part L 2021.  This data is provided by the Future Homes Hub and inferred from the software version used to generate the Energy Performance Certificates for the homes.  The dotted orange line is shifted three months as an estimate for roofing works going on, and solar panels being installed.

In December 2025, only 60% of homes that completed in England were built to Part L 2021 - some three and a half years after the regulations came into force.  How is this possible?

The clue to the answer to this question is found by looking at the black line.  There was an unusual spike in housing starts in the run up to the June 2023 cut-over date.  Housebuilders commenced nearly 30,000 more houses than in a normal quarter.  Strip foundations were excavated and concrete poured to classify plots as commenced.  These foundations were then mothballed for many, many months before being built on later - and locking in the older, and lower cost regulations.

What This Means for the FHS

The FHS imposes higher costs on developers, around £5,000 per house according to the Government's own Impact Assessment, so the incentive to delay the change over will definitely be there, just as it was for Part L 2021.  

There are a couple of potentially important differences this time around which may influence how long the transition takes.  

Firstly, the 2023 rush to lay foundations and beat the deadline for commencement occurred as mortgage rate increases precipitated a house buyers' strike.  The foundations lasted longer than they would have if the housebuilders were working at their usual rates.

Secondly, what counts as a "commencement" changed in late 2023 and now requires the first floor structure to be complete.  So for a house with a concrete slab ground floor, to the cost of the foundation you can now add the cost of building the below ground walls, a base-layer of hardcore and blinding and then pouring a concrete slab, plus all the drainage and service ducts required.

Will this second change be enough to change the financial calculations of the housebuilders - it's too early to say, but given the size of the prize from the cost saving, it's hard to see why the housebuilders won't rinse and repeat what they did for the 2021 regulations.

A sober assessment of how quickly the FHS will feed though to demand for more solar PV puts the start of the ramp in June 2028 and runs through to the end of 2030.

New Research Published - Rooftop Solar Reaction to Fire

Above Roof Solar PV Panels over (BRoof) Plastic Tile Roof - 8 Minutes into Test.
  Image: Health and Safety Executive 

The UK's Health and Safety Executive (HSE) has published a new report detailing a series of fire tests performed on pitched roof installations of solar PV panels.  The results (and the pretty spectacular photos) should give the solar and construction industries much to consider, as the findings challenge long-held assumptions about how fire safety regulations apply when solar is fitted to buildings.

In this blog we'll take a look at the tests and what they may mean for future regulation of the safety of  solar installations.

You can access the full HSE report on this link: Fire Spread Over Pitched Roofs Fitted with Solar Panels 

Key Findings

1. Above-roof solar is not immune to fire.  Above-roof solar contributes to the spread of the fire by providing fuel to the fire, and by changing the fire dynamics of the roof covering for the worse.
2. Roof-integrated solar systems based on plastic trays performed far worse than those without plastic trays.  The combustible plastic tray accelerated the fire which spread twice as far and twice as fast when compared to a proprietary roof integrated solar system of panels with a push-fit aluminium flashing that avoids the use of plastic trays.
3. Glass-glass modules perform better than those with a plastic back sheet but still got involved in the fire once the glass broke and plastic encapsulant material was available to the fire.
4. Current fire regulations do not address the risk posed by fires initiated by electrical faults in the solar installation (for example faulty DC-DC connectors) which highlights the value of fire safety products like ArcBox.

This project by the HSE is an extremely helpful contribution to the ongoing debate about how to make solar installations safer, and should encourage industry participants to consider solar practice that does more than just meet the current (insufficient) regulations instead of waiting for regulations to catch up.

None of the findings should have come as a surprise to folks in the solar industry - see the featured news articles below, but the fact is that most people in the solar industry would  just prefer not to spend time thinking about this topic.  

Which another way to say that we've probably lost most of our readers already, but lets plough on and dive into the detail of the report...

The Tests

A crib of burning wood was placed behind the bottom left panel in an installation of four solar panels.  The intention is that the crib simulates an electrical fault in a DC-DC connector.  The panels are on a test roof pitched up at 45 degrees.  Fans at the base of the roof are activated after 2 minutes to simulate the effect of a wind pressure on the roof.

A range of sample combinations were tested which combined above roof systems with different panel types and roof coverings as well as testing different roof integrated systems.  The time taken for the fire to spread to the top of the sample roof was recorded.  If the fire did not reach the top of the roof within 17 minutes the fire was extinguished and the spread of the fire spread was inspected after disassembling the installation.

Above Roof Solar

The working assumption in the solar industry has been that if you install solar on racks above a traditional roof covering, that the fire performance of that roof covering is unaffected and a new fire classification is not required for the roof build up including the solar panels.

The HSE report blows a massive hole in this.  

Firstly, the tests with solar panels installed above incombustible concrete tiles showed that the backing sheet of plastic on the rear of the panels will contribute to the development and spread of a fire.  Glass backed modules were found to perform much better than those with plastic back-sheet but still provided fuel from the cell encapsulant after the glass shattered due to the heat.

Second, the test with panels installed above plastic roof tiles had the fastest spread of flame of any of the tests and needed to be stopped after only 8 minutes because of safety concerns (this is the image at the top of the page).  These plastic tiles have a BRoof (T4) fire classification - the highest possible fire classification for a pitched roof covering. 

The presence of the solar panels above the combustible roof covering changes the fire dynamics, trapping heat and reflecting it back onto the fire as well as funnelling air over the fire (a chimney effect).  

The tests make clear what has been evident from real-world fires - that above-roof solar is not immune to fire and this is especially the case when installed over combustible roof coverings.  Note also that none of the tests attempted to simulate the real world situation where combustible material such as bird nests or wind blown leaves have accumulated behind the panels.

Real World Fires

St. Martin's Hospital, Bristol, UK, 22/05/2025 - fire spread behind above roof panels on flat roof of this maternity hospital, necessitating the evacuation of the building.

Bow Wharf, Bethnal Green, London, UK, 2/7/2017 -  fire behind panels installed above slate roof during the refurbishment of this building.

Roof Integrated Solar

Roof integrated solar systems replace tiles or slates on the roof.  Two types of system were tested.  One type that covers the roof with overlapping plastic plates before fixing the panels above, and a second that does not use plastic trays and fixes the panels straight to the roof with an aluminium surround (flashing) that pushes into the panels.

The system using plastic trays performed far worse in the tests, with the fire spreading to cover about twice the roof area in half the time compared to the system without plastic trays.  The explanation for this is the large quantity of accessible fuel for the fire provided by the plastic trays.  

A number of test were run with the plastic tray systems that varied the type of roofing membrane below the trays using membrane with differing fire rating.  The finding that this made no difference to the outcome suggests that the plastic tray is the main contributing factor for the very rapid spread of the fire.

Real World Fires

House Fire, Roden, Netherlands, 04/09/2023 - fire spreads on plastic tray roof integrated solar system with the seat of fire near the top of the array which limited the area of damage.

North Prospect, Plymouth, 03/05/2022 - fire destroys roof of new build residential property in Plymouth.  Fire partitioning prevents spread to joined house.

Does the Rate of Fire Spread Matter?

The average total response time by the Fire Service for a house fire in England in the period from 2013 to 2023 was an amazing 7 to 8 minutes.  The length of time the tests ran for, and the growth of the fire in that time is representative of how developed a fire would be when the Fire Service arrives at the building. The differences between the reaction to fire of the different systems could make a big difference to the scale of the challenge that the fire service faces upon arrival and the amount of damage done to the building by the fire and the measures to extinguish it.

Source: UK Home Office Official Statistics

Fire Regulations

The fire regulations relating to roofs were designed for a world where roof coverings were passive materials like concrete, clay, and slate and the risk that needed to be managed was to stop a fire next door spreading to your building.  Roofs are tested and classified for their reaction to an external fire outside the outermost layer of the roof covering.  Depending on the classification achieved, there may be limitations placed on the use of the roof covering (its proximity to adjacent buildings, the maximum continuous area of roof covered).

When solar panels are added on top of an existing roof covering, the interpretation has so far been that the roof covering below the panels performs as if the panels were not there and you can use the fire classification for the roofing material when tested alone.  

This work by HSE is just the latest in a line of research that has been sounding the alarm that this approach is not a safe one (see list below).  The presence of solar panels above the roof covering clearly does change the fire performance of the roof.

• Experimental Study of the Fire Behaviour on Flat Roof Constructions with multiple Photovoltaic (PV) panels. Fire Technol. 2018 Nov;54(6):1807–28.
• Experimental study of fire propagation on sloped roof with building applied photovoltaics. J Phys: Conf Ser. 2024 Nov 1;2885(1):012047.
• Impact of flat roof–integrated solar photovoltaic installation mode on building fire safety. Fire and Materials. 2019 Dec;43(8):936–48.

The current regulations are insufficient and should be urgently reviewed, but  regulatory change is painstaking and slow.   In the meantime schemes like the Microgeneration Certification Scheme in the UK could require fire classifications for above-roof solar systems, and put this in place more quickly than traditional regulations will manage.

Mitigation Measures

While we wait for the regulatory environment to catch up, should the solar industry just carry on as it is, sheltering behind the argument that its practices are 'compliant with regulations', regulations we now know to be insufficient for the situation?

Risk = Likelihood x Consequence

The research has focused in the consequence of a fire that starts in the solar installation and how fast it spreads in different situations.  You can also reduce the risk by lowering the likelihood a fault occurring, or if it does occur stop it spreading to start the fire in the first place.  Clearly higher-quality installations with fewer errors is a good starting point, but technical mitigation measures can be specified that in the event of an electrical fault, help prevent the development of a fire:

• The ArcBox DC connector enclosure protects the solar connectors in the installation from external damage and in the event of a fault contains arcing to prevent the initiation of a fire.
• Arc Fault Circuit Interrupt (AFCI) is a technology that uses electronic monitoring of the current in the solar circuit to detect the presence of an arc and disconnect the power.
• Micro inverters reduce the DC voltage in solar systems to a level below that which can cause arcing.

Conclusion

The findings of this research, and the other studies mentioned, make it hard to avoid the conclusion that the solar industry needs to do more to reduce fire risks.

• Solar installations above combustible roofing materials (including building integrated solar installations) could be required to adopt additional mitigation measures against situations where the fire starts in the solar installation itself.
• A new test for external fire performance of roofs could be developed to allow the fire classification of a roof including above-roof solar panels and mounting system. 

Warm Homes Fund to Go All-in on Solar

 Announcement in January Expected to Include Grants for Solar PV

Zero Bills Homes by Keepmoat and Platform Housing Group (C) Viridian Solar

It is widely expected that a £13bn 'Warm Homes Fund' to be announced by Ed Miliband in January will include grants for the installation of solar PV and batteries.  If so, this will represent a big departure from previous policy in this area which have almost exclusively emphasised retrofit insulation measures.

Until recently the accepted wisdom has been coined 'fabric first’.  This catchy phrase summarised a prevailing energy-efficiency orthodoxy which held that until you fix the insulation and airtightness of a building (its fabric) there is no point using ‘expensive bolt-ons’ like solar.  

Fabric first became sacrosanct for some in the energy efficiency industry (and not only those who manufacture insulation), with every consultation on building regulations met with howls of criticism from some quarters for not going far enough on required insulation levels and any inclusion of solar or other technology criticised as 'green bling'.  

Numerous government policies have been influenced by fabric first thought – with ECO, Low Carbon Buildings Programme, and most recently the ‘Scottish Passivhaus’ rabbit hole that building regulations north of the border appear to be about to disappear down all prioritising insulation over renewable energy.

This dismissal of solar bling as unserious and insulation as the only ideologically pure approach to decarbonisation misses three important points: 

First, that thermal efficiency is a game of diminishing returns.  

Second, (and linked to the previous point), having run out of easy targets such as loft and cavity wall insulation, more ambitious retrofit approaches aiming for big improvements in thermal efficiency can be highly invasive, complex and risk unwanted side effects like damp and mould.

Third, that the orthodoxy arose at a time when our energy system was dominated by fossil fuel and renewable energy was expensive.  This is now out of date.  What matters more today and in future is when you use energy not how much you use.

Diminishing Returns

It's physics.  The more you insulate a building the more difficult becomes the next improvement in performance, until you are adding large amounts of insulation for only marginal gains.  Building regulations for new homes appear to have now reached this point since the Future Homes Standard consultation proposes no change to the fabric performance of new homes over those of current (2021) regulations.

In retrofit scenarios, the payback for simple low cost measures like loft insulation chimney balloons, lagging hot water tanks and pipes and draft excluders is measured in months while more expensive improvements like external wall insulation for solid walls can take many years to pay back their costs.

Unwanted Side Effects

Once you've lagged every hot water cylinder, topped up loft insulation where you can and blown insulation into walls with cavities, you're left with a large number of hard-to-treat properties with solid brick or block walls.  These require a layer of insulation to be fixed to the external walls either on the inside face which makes the rooms smaller or on the outside face which needs to be carefully protected against the weather. 

The challenges with solid wall insulation really became apparent once we moved from theory and pilot studies to pushing into volume in the real world.  The work is complex, expensive and intrusive and has sadly proven to be easy to get badly wrong at scale, with unwanted side effects such as damp and mould widely reported. 

A National Audit Office review of works done under the ECO4 and the Great British Insulation Scheme found that an amazing 98% of homes fitted with external wall insulation and 29% of those with internal wall insulation had major issues that need fixing.

The Economics Has Shifted

Fabric first approaches to energy conservation in buildings emerged at a time when renewable energy was ruinously expensive and the energy supply system was dominated by coal, oil and gas.  At this time, the careful conservation of energy was the only logical way to reduce emissions and lower energy bills.

Renewable energy is now the cheapest form of energy.  It getting more and more plentiful as investments in new solar and wind capacity expands.  The nature of renewables is that the timing of generation cannot be controlled in the same way as it can for fossil fuel based energy, but the falling cost of battery energy storage and advent of smart controls that react to time-of-use pricing signals are combining to overcome the weakness of intermittency in renewable generation.

Those who can adjust their energy demand to use power when energy is in over-supply can now take advantage of these tariffs to pay very low (sometimes zero, sometimes negative) prices for their power.  Space heating, domestic hot water and electric vehicle charging are all amenable to time-shifting or rate shifting.

New housing developments such as Hollymead Square in Essex and Beeston Canalside in Nottingham offer so-called Zero Bills Homes where the combination of solar PV, battery energy storage and electric heating with time of use tariffs and smart energy controls allow the energy supplier, Octopus Energy, to guarantee that the householders will pay nothing for energy for ten years after moving in. 

In this approach to low-carbon living it's not how much energy you use, its when you use it and how you combine that with maximising the use of low cost renewable energy you generate for yourself.

Learn to Love the Bling 

The case for using energy sparingly has not gone away, and simple, low-cost insulation improvements will always be high up the to-do list.  

However renewable energy is combining with smart energy management, electrification of transport and heating and battery energy storage to offer an alternative vision in which the when of your energy use is as important as the how much.  If the Warm Homes Fund recognises this fundamental shift, then that is to be welcomed.

Fire Classification of In-Roof Solar PV

Housebuilders, building control inspectors and Microgeneration Certification Scheme (MCS) auditors should be alert to the increasing risk that roof-integrated solar mounting systems that use interchangeable solar panels from third-party manufacturers will be installed with solar panels for which the combined system has no fire classification.

Building Regulations and Fire Safety

In the early hours of Sunday morning, Thomas Farriner was awoken by smoke coming under the bedroom door.  His bakery downstairs was on fire.  It was September 2nd, 1666 and over the next four days this fire would spread, quickly jumping across the narrow lanes from one timber-framed building or thatched roof to another.  From its small start in that bakery in Pudding Lane, the Great Fire of London as it became known went on to destroy almost all of the medieval centre of the city.  

The responses to the disaster included the emergence of the first insurance companies, together with their own private fire-fighting organisations.  In addition there was a new focus on creating building codes with the aim of preventing the spread of fire between buildings.

The Rebuilding of London Act 1666 laid out restrictions on the type of building materials that could be used ("all Walls in front and reere as high as the first Story be of the full thicknes of the length of two Bricks").  It also increased the distance between buildings by requiring London's streets to be widened. 

You can draw a dotted line all the way from this first law regulating the construction of buildings to today's Building Regulations.

The UK Building Regulations Approved Document B outlines the legal requirements for fire safety. 

If on reading the Requirement you're wondering how you go about demonstrating compliance you wouldn't be alone - it's woolly isn't it?  Fortunately the regulations go on to lay out "Guidance".  In practice, for most situations, most people will seek to show that their building meets the Guidance because meeting the Guidance is a Matter of Fact, whereas trying to meet the Requirement by other means is a Matter of Opinion.

The Guidance Requires a Fire Classification

Section 12 of Approved Document B deals with roofs, outlining the situations in which roof constructions with varying fire classification can be used.  For example, roofing materials with a lower fire classification may only be allowed when installed more than a certain distance from boundaries and with limitations to the maximum area of roof covered.

The resistance of roofs to external fire exposure is measured in terms of penetration through the roof construction and the spread of flame over its surface.

Roof constructions are classified within the European system as BROOF(t4), CROOF(t4), DROOF(t4), EROOF(t4) or FROOF(t4) in accordance with EN 13501-5. 

BROOF(t4) indicates the highest performance and FROOF(t4) the lowest, whereas the (t4) indicates the use of Test 4 in the standard.

An alternative route to classification involves testing to a British Standard, BS476-3, with Approved Document B providing a 'transposition table' that allowed a classification to 476-3 to be treated as if equivalent to a given classification to 13501-5.

• If a roof covering does not have a fire classification, it is not possible to follow the guidance in the Approved Document to demonstrate compliance with the building regulations.
• The classification is for the whole roof system, so it is not possible to add fire-resistant layers to an unclassified system and assume a performance – the whole system including the fire-resistant layer must be tested together as a roof build up.  
• Building applied PV (on-roof) currently lives in a grey area where a fire classification for the roof without solar panels is assumed to be representative of the classification of the roof with solar installed above it - despite a growing body of evidence that building applied solar does change the fire dynamics of a roof.  (See, for example,  1,  2,  3)
• Building integrated PV is not in a grey area – it must have a fire classification to be lawfully used, unless an Alternative Approach is used, requiring a report from a Chartered Fire Engineer for each building the system is used on. 

Interaction with the Microgeneration Certification Scheme 

The Microgeneration Certification Scheme (MCS) approves and lists both solar panels and solar panel mounting kits.  To register a solar installation with the scheme, an MCS certificated solar installation company must use a certificated panel and combine this with a certificated mounting kit. 

As a condition of insurance (for example those offered to buyers of new homes by the likes of NHBC, LABC Warranty), many housebuilders require an MCS certificate for the solar installations on their developments.

The MCS12 standard deals with solar mounting kits and it requires that where such kits either replace roof coverings or create excessive gaps in roof coverings that a fire classification to BS EN 13501-5 of BS476-3 is obtained and declared.

Some roof-integrated solar systems are proprietary, combining a dedicated solar panel and mounting kit into a single system whose component parts cannot be interchanged, so that once tested and issued with a fire classification, non-compliant installations are not possible.

Other roof-integrated solar systems consist of a mounting system from one manufacturer that can be interchangeably combined with a solar PV panel from any number of other manufacturers.  The MCS12 standard requires that these mounting systems have a fire classification for each solar panel family it can be used with and that these panel families are listed on the MCS12 certificate.  A fire rating achieved with one panel family is not portable to another family, even those from the same panel manufacturer, because differences in Bill of Material for different panels have been shown to result in different performances in the fire tests.

The online system of registering an installation with MCS (called the MID) only allows the issue of a certificate if the installation comprises both an MCS certificated panel and an MCS certificated mounting system, but crucially it does not check that the solar panel model used with the mounting system is listed on its MCS12 certificate as having a combined fire classification.  This means that it is left to the solar installer to ensure that only listed solar panels are used in combination with the in-roof mounting kit.

• For roof-integrated solar systems that allow interchangeable panels, a loophole in the registration software makes it possible to obtain an MCS certificate for a non-compliant combination of panel and roof-integrated mounting kit for which there is no combined fire classification
• Consequently, the existence of an MCS certificate for roof-integrated solar installation proves neither that the system is compliant with MCS nor meets building regulations.

Recent Difficulties Obtaining New Fire Classifications for Solar PV Systems

In 2023 EN 15725 was updated.  This standard deals with the “extended application of fire performance of building products and building elements”.  The new version removed the ability of fire test laboratories to use expert judgement to extend fire classifications under EN 13501-5 beyond that which was tested,  and instead limited such extended application only to those situations specifically dealt with in the standard.

The new version of EN 15725 did not include extended application guidelines for the fire classification of solar PV roofing systems.  

Some fire experts have interpreted that the new version of EN 15725 completely prevents the fire classification of solar roofing, arguing that expert opinion is required to define the test conditions.  Other experts believe that testing can still proceed but that a classification can only be issued for the exact system that was tested –in effect limiting the fire classification to a single solar panel model rather than a whole solar panel family with a range of electrical powers as was previously the case.

In September 2023, many of the limited number of test laboratories that are capable of testing withdrew from issuing fire classifications for solar roofing systems, further refusing to test and classify to BS476-3 even though EN15-725 has no direct bearing on this standard.

Hopes were raised that a written opinion from the British Standards Institute (BSI) committee with responsibility for BS476-3 (FSH22-8) would convince reluctant fire testing laboratories to re-open the BS476-3 route to classification, but these  subsequently dashed when a change to Approved Document B removed any reference to BS476, leaving only the European classification as a means of compliance with the Building Regulations.

Both routes to demonstrating compliance with MCS012 and Building Regulations were closed. 

Meantime, the solar industry marches on with its relentless technological progress.  New solar panels are constantly being launched and older panels withdrawn from the market.  The in-roof solar market is insufficiently large to influence the product strategy of global solar manufacturers, for whom utility scale solar drives the greater part of demand.  

Existing fire classifications remain valid, but without a means to test and add new solar panels to their list, the number of products that are still available in the market with which those roof-integrated solar systems that use interchangeable modules have a combined fire classification is diminishing month by month.

Furthermore, the interest of housebuilders in innovations such as Octopus Energy's ‘zero bills homes’ programme has created a pressure to maximise annual solar generation from the roof by using the most up-to-date solar PV panels with the highest power-density (N-Type or TOPcon panels).  In almost all cases, these newer panels post-date the withdrawal of testing, so do not have a combined fire classification with the mounting systems.  

Confusingly, some of these newer panels have a power output in a smaller size (108 cell) that matches older, larger-area (120 cell) panels for which the roof-integrated system may have a combined fire classification.  Solar installers have mistakenly concluded that these newer panels have a fire classification when they do not, by not checking beyond the brand name and power rating to consider whether the actual product code for the panel is listed as having a fire classification. 

• The publication of a new version of EN 15-725 in 2023 caused test laboratories to suspend new fire classifications for new PV panel families with roof-integrated solar mounting systems
• The number of products that are still available in the market with which roof-integrated solar systems that use interchangeable modules have a fire classification is diminishing.
• Housebuilders, building control inspectors and MCS auditors should be alert to the rapidly rising risk that roof-integrated solar mounting systems that use interchangeable panels from third party manufacturers will be installed with panels for which they have no fire classification in combination.
• It is insufficient to check that the manufacturer and power level is listed as having a fire classification with such systems – the product code must match – as the classification listed may be for an older panel of the same power, but larger format (area).

How to Get Through This?

The MCS is leading the response to the challenges created by the publication of the new standard and the withdrawal from solar fire classifications by test laboratories.

One possibility, now underway, is to create a industry guidance document for the testing and certification of solar PV roofing systems.  The idea is that this document will outline a consistent approach that test laboratories can then use to apply the tests in TS1187 to solar roof samples.  It is important that, for it to be widely accepted, the guidance should be developed in consultation with all relevant stakeholders including the solar industry, fire test laboratories, the safety regulators (for all devolved governments) and building control.

The development of this document may require a series of fire tests to demonstrate the approach is rigorous.  Given this, and the number of bodies involved it is becoming obvious that this will be no quick fix.

However, you cannot finish what you do not begin, so it is good that there is an agreed approach and that a start has been made.

What Should the Industry do in the Meantime?

Choosing a proprietary roof-integrated solar system that does not allow the interchangeable use of solar panels from different manufacturers greatly reduces the risk, but you should still ask for evidence of the fire classification for the system.

When using a roof-integrated solar system where third party solar panels can be interchangeably substituted, ask the mounting system manufacturer to provide evidence that the exact model of solar panel you intend to use has a UK fire classification (not an indicative classification) in combination with this mounting system, and take steps to ensure that this model is not substituted at any time during the project.

In both cases the MCS012 certificate for the product concerned will have a list of the solar panel product codes with which the system has a fire classification.

Moving Fast - Solar Uptake on New Homes

 

New data provided by the Microgeneration Certification Scheme (MCS) shows that the proportion of new homes built in England that come with solar PV has more than doubled in the last 12 months.

In the last quarter of 2023 it was estimated that 13% of new homes that completed construction had solar PV fitted by the developer.  This figure has risen to 29% in the most recent quarter and will continue to grow as housebuilders in England further transition to the 2021 version of Part L of the Building Regulations.

As the number of new homes with solar PV built by private developers has increased, the average installed power (kWp) per new build installation is falling.  

Prior to the new Building Regulations coming into force, solar on new homes was driven by either local planning requirements or fitted by self-builders as a personal preference.  Self-builders would size a system for a cost-effective contribution towards their own energy requirements.  Solar to meet a planning condition was on a site-wide basis and tended to be concentrated onto a few homes on the development to meet the condition in the most cost-effective way.  

By contrast the new Building Regulations apply individually to each plot but once the required energy performance of the building is met, developers generally see little reason to extend a PV system further - resulting in generally smaller PV installations.  The effect of this can be seen in the kWp/install column where the average has reduced over the period from 3.8kWp per installation to 2.8kWp.

Also worth noting is that solar on new buildings has risen from being 19% of MCS certified solar installations in England to 34% over the period.  As already mentioned, this transition has further to run and I predict that by the end of 2025, new build solar will account for at least 50% of MCS solar installations in the UK.

Notes on the Analysis

The number of new build MCS solar PV installations in the quarter was expressed as a proportion of new build housing completions in the same period to arrive at a percentage of new homes built with solar PV.

When registering a new solar PV installation with the MCS, the installer must tick a box to say whether the installation is on a new building.  The brilliant, publicly available MCS data dashboard does not currently allow users to filter the data on this basis, but the team at MCS responded to a request from Solar Energy UK and kindly provided us with the data.  I hope this functionality can be added in future.

The MCS certificate is issued only when the system is commissioned, which occurs after second fix.  This creates the potential for a timing difference between the MCS data and the data based on practical completion of the building (which may come a few weeks later).  The error this creates is mitigated against by aggregating to quarterly data.

It is also worth mentioning that it was not possible to split the MCS new build data into residential and commercial installations, so I have had to assume that the total is all residential, which will result in an over-estimate, but one that reduces as the number of new build homes with solar grows.  On the other hand not all solar installations will run through the MCS so this mitigates the over-estimate, as does focusing on the number of installations rather than the installed power (commercial solar tends to be larger systems in lower number).

Data for housebuilding completions is taken from this ONS dataset, which is quarterly, and only available up to Q2 2024.  The dataset was extended by one quarter by reference to this NHBC data which was used to scale the figure for Q2 to Q3.